Background

Cancer pain is a pervasive clinical symptom impairing life quality. Vascular endothelial growth factor A has been well studied in tumor angiogenesis and is recognized as a therapeutic target for anti-cancer treatment. This study tested the hypothesis that vascular endothelial growth factor A and vascular endothelial growth factor receptor 2 contribute to bone cancer pain regulation associated with spinal central sensitization.

Methods

This study was performed on female rats using a metastatic breast cancer bone pain model. Nociceptive behaviors were evaluated by mechanical allodynia, thermal hyperalgesia, spontaneous pain, and CatWalk gait analysis. Expression levels were measured by real-time quantitative polymerase chain reaction, western blot, and immunofluorescence analysis. Excitatory synaptic transmission was detected by whole-cell patch-clamp recordings. The primary outcome was the effect of pharmacologic intervention of spinal vascular endothelial growth factor A/vascular endothelial growth factor receptor 2-signaling on bone cancer pain behaviors.

Results

The mRNA and protein expression of vascular endothelial growth factor A and vascular endothelial growth factor receptor 2 were upregulated in tumor-bearing rats. Spinal blocking vascular endothelial growth factor A or vascular endothelial growth factor receptor 2 significantly attenuated tumor-induced mechanical allodynia (mean±SD: vascular endothelial growth factor A, 7.6±2.6 g vs. 5.3±3.3 g; vascular endothelial growth factor receptor 2, 7.8±3.0 g vs. 5.2±3.4 g; n= 6; P< 0.0001) and thermal hyperalgesia (mean±SD: vascular endothelial growth factor A, 9.0±2.4 s vs. 7.4±2.7 s; vascular endothelial growth factor receptor 2, 9.3±2.5 s vs. 7.5±3.1 s; n= 6; P< 0.0001), as well as spontaneous pain and abnormal gaits. Exogenous vascular endothelial growth factor A enhanced excitatory synaptic transmission in a vascular endothelial growth factor receptor 2-dependent manner, and spinal injection of exogenous vascular endothelial growth factor A was sufficient to cause pain hypersensitivity via vascular endothelial growth factor receptor 2-mediated activation of protein kinase C and Src family kinase in naïve rats. Moreover, spinal blocking vascular endothelial growth factor A/vascular endothelial growth factor receptor 2 pathways suppressed protein kinase C-mediated N-methyl-D-aspartate receptor activation and Src family kinase-mediated proinflammatory cytokine production.

Conclusions

Vascular endothelial growth factor A/vascular endothelial growth factor receptor 2 contributes to central sensitization and bone cancer pain via activation of neuronal protein kinase C and microglial Src family kinase pathways in the spinal cord.